| Summary: | 碩士 === 國立成功大學 === 工程科學系碩博士班 === 100 === In this experiment, we demonstrate production of a microfluidic chip through a micro-electromechanical technique and, by use of Nafion instead of a nanochannel, we produce integrated micro-nano chips for use in sample preconcentration. By applying an electric field to the chips, the Nafion becomes ion selective as a result of inner electric double layer overlapping. More specifically, when a difference in flux exists between positive and negative ions in the nanochannels, it results in a concentration polarization phenomenon at the micro and nano interface. Concentration polarization phenomena cause a concentration gradient to occur near the membrane.
This study used an ion-selective membrane in which the flux of the cation is larger than the flux of the anion. When we applied an electric field, the effect caused a partial depletion at the anodic side and ion enrichment at the cathodic side. The ion accumulation is induced by the difference in electromigration at the border between the depletion zone and electroosmosis flow. In the end, it creates a high concentration interface in the channel.
In this experiment, we will discuss how geometric factors influence preconcentration through a straight microchannel and a convergent microchannel. A convergent channel is in the middle of a channel and narrows the width, so that the sample can be concentrated in smaller areas by the impact of different flow rates. As a result, the fluorescence concentration increases in this reduced unit area.
We hypothesized relatively faster and more efficient concentration at higher voltages, and thus used the potential difference to study ways to enhance the feasibility of the preconcentration effect in this device, thereby optimizing the device. Based on the experimental result, we took the applied voltage of 50 V in this experiment. To confirm how it works in the preconcentration process, a fluorescein dye was used. To explore its applications in biomedical detection, we used FITC-labeled bovine serum albumin samples to observe the cumulative effect in the same device. In the experiment using a straight microchannel, FITC-labeled bovine serum albumin accumulated up to 100-fold in 360 s. With a convergent microchannel whose middle was 50 μm wide, the result showed that one can achieve a 200-fold increase in preconcentration factor within 840 s. With a convergent microchannel whose middle was 25 μm wide, the result showed that a preconcentration factor of at least a 400 had been achieved within 240 s.
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